Concrete sandwich panels are well known in the art, and generally comprise spaced apart layers of concrete with an insulation layer sandwiched between the concrete layers. Connectors extend through the insulation layer and into the concrete layers to tie the concrete layers together when the concrete cures.
Concrete sandwich panel connectors normally are supplied with deformations or anchorage zones to provide notches, bosses, or other irregularities in the connector. Such connectors are usually installed in highly plastic concrete, which can flow into or around the deformations in the connectors, such that, upon hardening of the concrete, the connector and concrete are locked together. The consolidation of the concrete flowing into and around the irregularities in the anchorage zones of the connectors creates a mechanical interlock between the connector and the concrete.
In contrast, when sandwich panel connectors are installed in stiff or dry concrete, such as dry-cast concrete, the concrete is not capable of flowing into and around the irregular surfaces on the anchorage zones. Rather, the connectors create a hole in the concrete that remains after installation of the connectors. The connectors therefore are not anchored to the concrete, and can be easily pulled out with little or no load.
Extrusion is a common method used to produce lightweight, economical pre-cast concrete floor and wall panels. The extruded concrete normally includes longitudinal voids, or cores, such that the panels are commonly called xe2x80x9chollow-core panels.xe2x80x9d Machines are used to slip form concrete with zero or low-slump into such hollowcore panels. Zero or low-slump material generally is defined as material having 0-1 inch of slump using standardized ASPM slump testing. This concrete, while including water or moisture, is very dry, and therefore will not flow around the sandwich panel anchorage zones. This concrete is commonly called xe2x80x9cdry-cast.xe2x80x9d
For this type of hollowcore panels, it is common to form sandwich panels using steel or stainless steel clips that must be anchored by hooking one end of the clips around a steel pre-stressing strand which is placed in the hollowcore layer during slip forming. In order to access the strand, the cured hollowcore concrete is excavated, and the connectors hooked around the exposed strand. The resulting hole in the hollowcore panel is then patched around the installed connector. This work is highly labor intensive and fails to provide a reliable anchorage of the connector in the concrete. The hooks of such steel clips can be straightened with a relatively small force, compared to the tensile capacity of the wire itself. Therefore, the pullout capacity of such anchorage clips is small. Also, the repair to the excavated concrete may leave voids around the wire clips. Since the wire clips are not embedded in the concrete, the clips are free to slide down the steel reinforcing strands in the hollowcore panel. This creates serious problems during handling and installation of the sandwich panels, with the face layer shifting more than an inch as the panel is moved to a vertical position. Furthermore, the excavation process can lead to zones within the panel wherein the reinforcing steel is not encased in the concrete. Because concrete creates a protective environment that slows the corrosion process for embedded steel, and because condensation is a common occurrence in sandwich panels, there is a serious probability that the reinforcing steel within the hollowcore panels will corrode and fail as a result of the installation of the hooked sandwich panel connectors or clips.
The installation of anchors or connectors in cured concrete using two-part epoxy adhesives is known in the art. This installation process requires that holes be drilled into the hardened concrete, which is highly labor intensive and time consuming.
Accordingly, a primary objective of the present invention is the provision of an improved dry-cast concrete hollowcore sandwich panel.
A further provision of the present invention is the provision of an improved hollowcore sandwich panel having connectors consolidated in the concrete layers.
A further objective of the present invention is the provision of a connection system that can be installed in dry or low-slump concrete.
Another objective of the present invention is the provision of a process for installing connectors in hollowcore sandwich panels.
A further objective of the present invention is the provision of a connection system, and a process for installing the connection system, that is positively anchored in the concrete layers of a sandwich panel, and does not allow large shear displacement of one layer of concrete relative to the other.
Another objective of the present invention is a concrete sandwich panel, and a method of producing the panel, without voids around the reinforcing steel strands contained in the panel.
A further objective of the present invention is the provision of hollowcore sandwich panels having a connection system with low thermal conductivity.
Still another objective of the present invention is the provision of hollowcore sandwich panels that the insulation system provides a uniform, verifiable spacing for the connectors.
Another objective of the present invention is the provision of a hollowcore sandwich panel having an improved concrete connection system.
A further objective of the present invention is the provision of a method for installing a connection system into a hollowcore sandwich panel utilizing minimum labor costs.
Another objective of the present invention is the provision of a hollowcore concrete sandwich panel that is economical to manufacture, and durable and efficient in use.
The concrete sandwich panels of the present invention include a first hollowcore concrete layer and a spaced apart second concrete layer. Insulation is sandwiched between the concrete layers. Preferably, the hollowcore layers are constructed by slip forming zero or low-slump material, so as to have a plurality of voids and concrete webs. The hollowcore layer includes pre-stressing strands in some of the webs. The insulation layer includes a plurality of preformed holes. Holes are formed in the hollowcore layer before the concrete hardens and in alignment with the insulation holes. Adhesive, preferably a two-part epoxy or acrylic, is injected or otherwise supplied into the holes in the hollowcore layer. The adhesive provides a strong bond between the connector and the hollowcore layer. Connectors having low thermal conductivity are inserted through the insulation holes and into the holes in the hollowcore layer. A second concrete face layer is formed on top of the insulation, with the opposite ends of the connectors extending into the face layer, which consolidates around an anchoring surface on the upper end of the connectors.